Connor Barwin and the Eagles' D are ranked 30th in the league this season. (AP)

The kind of “shock the world” and “chance of a lifetime” rhetoric coming from the Eagles’ locker room Tuesday isn’t usually reserved for Week 4 games against non-conference opponents.

Must be something about this Peyton Manning fella that has the Eagles’ defense a little extra geared up.

“It’s an opportunity of a lifetime, man. This is the zenith of football,” said cornerback Cary Williams, who spent just about the entire 45 minutes of open locker room after Tuesday’s practice with reporters huddled around his space, talking about Sunday’s showdown against the Broncos in Denver.

“It’s a wonderful opportunity for us to go out and shock the world. It’s a great opportunity. I don’t see it as as, ‘Aw, damn, we got them on the schedule.’ I see it as, ‘Damn, we got them on the schedule, let’s make it happen.’ It’s a wonderful opportunity.”

The sad reality for the Eagles' defense is that Sunday is their Super Bowl. Popular perception is that Manning will add another quartet or so of touchdown passes to his growing list, which reached 12 in Monday night’s blowout of Oakland, an NFL record after the first three weeks (see story).

Vegas has set a ridiculously high over-under number (see story), daring the public to bet on Billy Davis’ struggling group.

“That’s the best situation to be in,” cornerback Brandon Boykin said. “Everybody knows and everybody is going to say we’re the underdog and everybody is looking for them to just come out and put up crazy points on us. As a defense, we take that to heart.

“We know Peyton is a good quarterback, we know they’ve got all these great offensive weapons. But that doesn’t matter. It’s not about what they do, really, it’s about what we do. When you have that mindset you become the enforcer and dictator. If we get a good pass rush and we’re able to hold our coverages and keep our disguises, we’ll be fine.”

If the Eagles were to execute the way Boykin laid it out, it would be their first time this season. When Manning jogs out onto the Mile High field, he’ll be staring down the NFL’s 30th-ranked defense. The Eagles are allowing close to 29 points per game, and Denver is scoring 42.

There were signs of improvement in Thursday’s 26-16 loss to the Chiefs, which the Eagles have chosen to emphasize. They allowed just six third-down conversions in 18 attempts, a 33-percent clip, and were especially effective in the red zone, where Kansas City scored one touchdown in six trips.

“We have everything to gain,” linebacker Mychal Kendricks said. “Not saying we don’t have nothing to lose, but we have everything to gain. This is a game [where] we can get better and it’s a game we need to win, and that’s what we plan on doing.”

Although Williams tried to paint the iconic Manning as another quarterback who laces up his cleats no differently than he does, he also called Manning “the greatest quarterback of our decade, arguably” and referred to the showdown as “an opportunity of a lifetime.”

Williams dismissed the notion that he and his teammates must fight a defeatist attitude, even if the forecast is a lopsided outcome.

“I don’t even think there’s any guy that has that mentality here,” he said. “I hope not. If [they] do, they need to take the [pay]checks away. Seriously.”

Williams is one of six Eagles starters who can actually claim a victory against Manning, and one of two since Manning signed with the Broncos last year after the Colts severed ties with the 11-time Pro Bowler and moved on to Andrew Luck.

Nate Allen and Trent Cole were each starters for the Sean McDermott-led Eagles defense that held Manning to a touchdown and picked him off twice in a 26-24 win at the Linc. Free safety Patrick Chung, who missed Tuesday’s practice with an injury, beat Manning as a Patriot in a 2010 game.

Connor Barwin and DeMeco Ryans were each on Houston defenses that got the best of Manning at least once. Barwin’s win came last year, when his Texans squad held Manning to a season-low 50-percent completion rate in beating Denver 31-25 at Sports Authority Field, the Broncos’ only regular-season home loss.

Barwin said the Texans didn’t concoct some “magic formula” to conquer Manning, because one doesn’t exist.

“We didn’t shut him down,” he said. “We shut him down for about three quarters -- and then I remember he kind of lit us up a little bit at the end. But it was a little too late. I hope it’s very similar [Sunday].

“It’s about what you do. Some guys you play, you make some mistakes, some quarterbacks don’t find it. This guy, you make a mistake he’ll find it. So it’s important you do what you do real well.”